Microwave oscillator



Aug. 20; 1957 c. L. ANDREW 2,803,749

MICROWAVE OSCILLATOR Filed June 18,1952

' Ir'wven tori ChClTlS L. Andrews,

His Attorney.

wi h! Eva: iuvvn-u MICROWAVE OSCILLATOR Charles L. Andrews, Albany, N. Y., assignor to General Electric Company, a corporation of New York Application June 18, 1952, Serial No. 294,118

3 Claims. (Cl. 250-36) My invention relates to microwave oscillators and has particular reference to resonant cavity apparatus for use with discharge device triodes.

Electron discharge devices have been adapted for use in the higher frequency ranges by minimizing the electrode lead length and by arranging the device electrodes so that the device can be incorporated in a resonant cavity in such a way that it forms a part of the cavity structure, both electrically and physically. In one class of discharge devices constructed in accordance with these objectives the various electrodes are disk-like planar cathode, grid, and anode electrodes spaced along a principal axis in parallel planes. Such devices are adapted for use with concentric line cavity resonators and in an oscillator arrangement may be effectively utilized in cooperation with coaxial cathode-grid and grid-anode resonators having feedback means between them. By removing the feedback coupling loops or probes from the grid-anode cavity, the cavity dimensions may be made as small as the mechanical arrangement of the discharge device will permit for higher frequency operation. It has accordingly been found desirable to incorporate feedback means which do not restrict the oscillator high frequency operation.

It is therefore an object of my invention to provide an improved concentric cavity oscillator.

It is a further object of my invention to provide an improved concentric cavity feedback means permitting higher frequency operation.

Briefly stated, in accordance with my invention, feedback coupling from a grid-anode resonator in apparatus of the nature described is provided by an energy leakage path along the anode terminal, which terminal extends into an outer cavity resonator and subsequently to an anode voltage source. The space or dielectric defining the leakage path also is a means for providing direct current insulation of the anode.

For additional objects and advantages, and for a better understanding of the invention, attention is directed to the following description and accompanying drawing. The features of the invention which are believed to be novel are particularly pointed out in the appended claims. The single figure of the drawing is a view, partly in cross section of oscillator apparatus embodying my invention. The apparatus is drawn to approximately /2 times actual size.

Referring now to the figure, a discharge device 1 is shown therein positioned in a concentric cavity resonator apparatus to provide a microwave oscillator. The discharge device is of the type in which the active surfaces of the cathode, grid, and anode are arranged in parallel planes, the electrodes being symmetrical about a common axis. The discharge device shown in the figure is described in detail and claimed in an application Serial No. 179,859, filed August 16, 1950, by James E. Beggs, now Patent No. 2,680,824, and assigned to the assignee of the present application. For the purposes of appreciating the operation of the device therein specifically de States Patent 0 scribed in the present invention, a brief description of the device 1 follows.

The active electrode surfaces of the device 1 are the cathode 3, the grid 4, and the anode 5, arranged in that order. The cathode 3 is a cylindrical member whose end surface facing the grid 4 is heated by an internal heater to provide an electronic space charge. The external terminal for the cathode is the cathode cylinder 6 which is concentric with the lengthwise axis of the device. A heater terminal 7 for one end of the cathode heater, the other end being attached to the cathode, extends through the center of the cylindrical cathode terminal 6 and is insulated therefrom for connection to a suitable source of heater voltage. The grid 4 preferably takes the form of a flat washer having a plurality of grid wires stretched across its central aperture for controlling the electron space charge. The outer edge of the washer is conductively secrued to a cylindrical grid terminal 8 concentric with the tube axis. The anode preferably takes the form of a conductive plate or disk of approximately the diameter of the grid washer opening and has a central rod-like terminal extension 9 extending along the device axis. Annular insulating members 10a and 1%, which may be suitably made of a ceramic material, are respectively sealed between each end of the grid terminal 8 and the cathode terminal 6 and the anode terminal 9. The discharge device 1 is designed to be capable for use with the tubular conductors of concentric conductor circuits at frequencies of 4000 megacycles per second and higher, and when employed in oscillator apparatus embodying my invention operating frequencies above 9000 megacycles have been obtained.

The resonator system comprises a hollow outer conductor 11 which surrounds a composite inner conductor which includes a cathode coupling condutor 12, an inner hollow conductor 13, and an anode coupling conductor 14. The space between the outer conductor 11 and the composite inner conductor defines the cathodegrid cavity resonator which may be visualized in a more simplified form as a concentric conductor cavity resonator having a gap in the inner conductor or between the end of the inner conductor and one end of the outer conductor. This gap is the cathode to grid spacing of the discharge device 1. The various conductors of the resonator system are made of brass or other suitable metals.

As further shown in the figure, an annular end conductor 15 between one end of the outer conductor 11 and the cathode coupling conductor 12 terminates the lefthand end of the cavity. The conductor 12 engages the cathode terminal 6 and is preferably provided with spring contact fingers for that purpose. The conductor 12 is relatively short and may, if desired, be reduced further in length so that the cathode contact terminal 6 is inserted directly into the annular end member 15. The other end of the input cavity between the outer conductor 11 and the anode coupling conductor 14 is effectively terminated by another annular conductive member 16. An insulating washer 17 positioned between the annular member 16 and the externally extending portion 18 of the anode terminal isolates the anode for applied direct current potentials. The inner end of the anode coupling conductor 14 engages the anode terminal 9 of the device 1, being suitably provided with spring contact fingers for that purpose.

While some capacitive coupling of the anode to the end surface 16 is provided by the proximity of the anode terminal portion 18, this coupling is very greatly increased by a radial flange 19 on the anode coupling conductor 14 which is spaced a very small distance from the inner surface of the end conductor 16. A thin mica washer 20 is utilized to maintain the spacing. In this way the leakage of energy from the cavity resonator along the anode terminal 14 is also minimized due to the small spacing between the flange 19 and the end member 16. It should be understood that while the flange 19 is shown as a relatively thin member, it may be extended in length if desired to form a substantial portion of the length of the inner conductor of the cathode-grid resonator.

In accordance with my invention, the hollow conductor section 13 serves both as part of the inner conductor of the cathode-grid cavity and as the outer or peripheral conductor of a grid-anode cavity resonator. As may be seen in the drawing, the conductor section 13 is a capshaped member whose cylindrical flange is dimensioned to surround the anode 5 and conductively engage the grid terminal cylinder 8 of the discharge device 1. The end wall 21 of the conductive cap 13 is centrally apertured to permit passage of the anode rod 9 therethrough with contact between them. The enclosure defined between anode 5 and the cylindrical portion of the conductor section 13 and terminated at its ends by the grid 4 and the annular end portion 21 defines the grid-anode cavity.

In order to conveniently limit the energy leakage from the grid-anode resonator along the anode terminal 9, a conductive washer 22 having its inner periphery engaging the anode terminal is positioned against the ceramic member at the anode end of the device 1. A thin mica spacer 23 between the end portion 21 of the cap 13 and the washer 22 provides a limited energy leakage path or passage between the resonators. While the grid-anode cavity can be considered as concentric with the coaxial cathode-grid cavity, it is believed to oscillate in a radial or intermediate mode due to the short distance between the grid and washer 22 rather than in a coaxial mode as does the outer cavity.

Inasmuch as the grid-anode cavity is designed to be as small as possible without allotting space for coupling loops or probes, feedback energy from this cavity is coupled to the other cavity through the passageway mentioned and between the anode rod 9 and the aperture in the end wall 21 of the conductor cap section 13. Energy thus transmitted tends to propagate along the anode lead. Since the anode terminal 9 is exposed to the outer cavity for a material distance, the fringing high frequency field thus introduced into the outer cavity provides suflicient feedback coupling for oscillation. At the same time, high frequency power leakage from the outer cavity along the anode conductor 18 is separately governed by the length and thickness of the path defined through the mica space 20 previously described.

In operation, a source of voltage 24 is connected between the end of the anode lead 18 and the outer resonator 2, and a source of heater voltage 25 is connected between the outer resonator and heater terminal 7, the outer conductor 11 being grounded for convenience. The grid 4 of the discharge device 1 is preferably connected to the outer conductor 11, for grounded grid operation and accordingly a connecting rod 26 which may suitably take the form of a threaded screw is threaded through an aperture in the outer conductor 11 at a point opposite the inner conductor 13 so that it may make contact therewith. An output coupling means 27 is utilized to transfer the output power from the resonant system to the desired load. This output coupling means may suitably take the form of a concentric conductor section whose outer conductor 28 engages the outer conductor 11 of the outer resonator and whose inner conductor 29 extends through an aperture in the conductor 11 to provide an inductive coupling loop in the cathode-grid resonator.

Since the resonant frequency of the grid-anode cavity is very critical with respect to small changes in the cavity dimensions, the cathode-grid cavity may be tuned to match this frequency through careful adjustment of the axial position of the transverse disk 16. The size of the cavities is not the same, however, and need not be, since the smaller cavity is believed to resonate in a one-quarter wave mode whereas the larger cavity may operate in a higher frequency mode, such as a seven or nine quarter wave mode.

While the present invention has been described by 5 reference to a particular embodiment thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the invention.

I, therefore aim in the appended claims to cover all 10 such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A microwave oscillator comprising a pair of concentric hollow conductors extending along a given axis,

an electron discharge device having parallel plane, cathode, grid and anode electrodes aligned in that order along said axis, an envelope enclosing said electrodes, said anode electrode including a portion extending through said envelope, the inner conductor of said concentric conductors surrounding said grid and anode, and engaging said grid electrode, said inner conductor including an inwardly extending flange having an opening therein through which the extending portion of said anode electrode passes,

an outwardly extending flange supported from the extending portion of said anode in spaced relation to said inwardly extending flange, an annular insulating member provided between said flanges to provide a capacitive coupling therebetween, conductive means between one end of 30 the outer conductor and said cathode, an axial conductor having one end engaging said anode, conductive means extending from the other end of said outer conductor towards the other end of said axial conductor, said axial conductor having located thereon an annular conductive flange member, and an annular insulating member provided between said flange and said conductive means, @yvhereby capacitive coupling is provided between said node and said outer conductor.

. 2. A microwave oscillator comprising a pair of concentric hollow conductors extending along a given axis, an electron discharge device having parallel plane, cathode. grid and anode electrodes aligned in that order along said axis, an envelope enclosing said electrodes, the inner conductor of said concentric conductors being electrically connected to said grid, direct electrical connecting means provided between said outer conductor and said inner conductor, said inner conductor including an inwardly extending end wall having an opening therein through which a portion of said anode electrode extends, a conducting flange extending outwardly from said portion of said anode electrode adjacent said envelope and in closely spaced relation with respect to said end wall, an annular insulating member provided between said end wall of said inner conductor and said flange to establish a capacitive coupling therebetween, conductive means interconnected between one end of the outer conductor and said cathode, an axial conductor having one end engaging said anode, conductive means extending from the other end of said outer conductor towards the other end of said axial conductor, said axial conductor having located thereon an anode electrode including a portion extending from said envelope, the inner conductor of said concentric lconductors being electrically connected to said grid and including an inwardly directed end wall having an opening therein through which the extending portion of said anode passes,

said extending portion having an outwardly extending flange adjacent said envelope and in closely spaced relation to said end wall, the outer conductor of said concentric conductors being electrically connected to said cathode, a conductive element depending within said outer conductor and electrically connected to said anode, an annular insulating member provided between said conductive element and said outer conductor, means extending within said outer conductor for deriving a signal from said oscillator, and connecting means provided between said outer conductor and said inner conductor, said 10 2,619,597

connecting means including a conductive member threadedly engaged with said outer conductor so as to be adjustable therewith to electrically connect said inner and outer hollow conductors.

References Cited in the file of this patent UNITED STATES PATENTS 2,421,784 Haeseler June 10, 1947 2 2,443,907 Gurewitsch June 22, 1948 Mlynczak Nov. 25, 1952 

